In recent years, a locking device for locking/unlocking a door of a car, a house, or the like by remote control is being practically used. A technique related to such a locking device is disclosed in, for example, Patent Document 1.
FIG. 9 is a configuration diagram showing an example of a conventional locking device used for a car. FIG. 10 is a diagram showing a control procedure performed in a case where a key exists on an outside of a car in a conventional locking device. Hereinafter, a car as shown in FIG. 9 will be taken as an example, and a conventional locking device of this type will be described.
First, a user of car 2 having key 6B touches a touch button 1 shown in FIG. 9 from an outside of car 2. As shown in FIG. 10, all-key ringing signal 5 is generated from car interior transmission antennas 4A and 4B having communication range 2A in car 2. However, since key 6B does not exist in communication range 2A, key 6B does not respond to the signal. Information thereof, that is, information that key 6B does not exist in the car is stored in a storage (not shown) in car 2.
Next, all-key ringing signal 12 is generated from car exterior transmission antenna 5C having communication range 2B including the outside of car 2. Since key 6B exists in communication range 2B, key 6B receives all-key ringing signal 12. Key 6B transmits response signal 13B to all-key ringing signal 12 to reception antenna 8 of car 2. In the storage in car 2, the information that key 6B exists on the outside of the car is stored. Consequently, individual authentication ringing signal 14 is transmitted from car exterior transmission antenna 5C to key 6B. In a case where key 6B receives this individual authentication ringing signal 14 and collation with a security code stored in key 6B is obtained, key 6B transmits individual authentication response signal 15. By the information, it is recognized that key 6B exists on the outside of car 2.
Accordingly, an unlock instruction or a lock instruction is given to the lock of the door in car 2. That is, the user having key 6B can control a state of the lock.
On the other hand, if a third party touches touch button 1 shown in FIG. 9 when the user of car 2 having key 6A stays in car 2, all-key ringing signal 5 is generated from car interior transmission antennas 4A and 4B having communication range 2A in car 2. Key 6A existing in communication range 2A receives all-key ringing signal 5 and transmits response signal 7 to reception antenna 8. When reception antenna 8 receives response signal 7, individual authentication ringing signal 9 is transmitted from car interior transmission antennas 4A and 4B to key 6A. In a case where key 6A receives individual authentication ringing signal 9 and collation with a security code stored in key 6A is obtained, key 6A transmits individual authentication response signal 10. Consequently, information that key 6A exists in the car is stored in the storage in car 2.
Next, car exterior transmission antenna 5C having a range including the outside of car 2 as communication range 2B thereof generates all-key ringing signal 12. Key 6A existing in communication range 2B receives this all-key ringing signal 12 and transmits response signal 13A to all-key ringing signal 12 to reception antenna 8 of car 2. However, since the information that key 6A exists in the car is stored in the storage in car 2, individual authentication ringing signal 14 is not transmitted from car exterior transmission antenna 5C to key 6A. Therefore, the lock of the door is uncontrollable and the third party cannot open the door of car 2.
FIG. 9 shows a configuration example in which car exterior transmission antennas 5A and 5B having a function similar to that of car exterior transmission antenna 5C are further mounted.
As described above, the conventional locking device had a configuration such that by transmitting all-key ringing signal 5 to an inside of car 2 before transmitting all-key ringing signal 12, nonexistence of keys 6A, 6B, 6C, and 6D in car 2 is confirmed and whether the locking control is enabled or not is determined. With such a configuration, the conventional locking device takes a measure for security to prevent a third party from opening the door in a case where the user having key 6A stays in car 2.
In the above-described conventional configuration, to specify an area where keys 6A, 6B, 6C, and 6D exist, as shown in FIG. 10, whether there is a response by a response signal from keys 6A, 6B, 6C, and 6D or not is determined. Consequently, reception has to be attempted twice. Specifically, reception of both response signal 7 to all-key ringing signal 5 from car interior transmission antennas 4A and 4B and response signals 13A and 13B to all-key ringing signal 12 from car exterior transmission antenna 5C is attempted, and each of the areas where keys 6A, 6B, 6C, and 6D exist has to be specified. As a result, communication time is long. As described above, the conventional locking device has problems that long communication time is necessary.    Patent Document 1: Unexamined Japanese Patent Publication No. 2003-20837